Ethnologue identifies 168 Austroasiatic languages. These form thirteen established families (plus perhaps Shompen, which is poorly attested, as a fourteenth), which have traditionally been grouped into two, as Mon–Khmer and Munda. However, one recent classification posits three groups (Munda, Nuclear Mon-Khmer and Khasi–Khmuic)[4] while another has abandoned Mon–Khmer as a taxon altogether, making it synonymous with the larger family.[5]

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The Austroasiatic languages are well known for having a "sesquisyllabic" pattern, with basic nouns and verbs consisting of a reduced minor syllable plus a full syllable. Many of them also have infixes. The Austroasiatic languages are further characterized as having unusually large vowel inventories and employing some sort of register contrast, either between modal (normal) voice and breathy (lax) voice or between modal voice and creaky voice.[7] Languages in the Pearic branch and some in the Vietic branch can have a three- or even four-way voicing contrast. However, some Austroasiatic languages have lost the register contrast by evolving more diphthongs or in a few cases, such as Vietnamese, tonogenesis. Vietnamese has been so heavily influenced by Chinese that its original Austroasiatic phonological quality is obscured and now resembles that of South Chinese languages, whereas Khmer, which had more influence from Sanskrit, has retained a more typically Austroasiatic structure.

Much work has been done on the reconstruction of Proto-Mon–Khmer in Harry L. Shorto's Mon–Khmer Comparative Dictionary. Little work has been done on the Munda languages, which are not well documented. With their demotion from a primary branch, Proto-Mon–Khmer becomes synonymous with Proto-Austroasiatic.

This is identical to earlier reconstructions except for *ʄ. *ʄ is better preserved in the Katuic languages, which Sidwell has specialized in. Sidwell (2011) suggests that the likely homeland of Austroasiatic is the middle Mekong, in the area of the Bahnaric and Katuic languages (approximately where modern Laos, Thailand, and Cambodia come together), and that the family is not as old as frequently assumed, dating to perhaps 2000 BCE.[6]

Linguists traditionally recognize two primary divisions of Austroasiatic: the Mon–Khmer languages of Southeast Asia, Northeast India and the Nicobar Islands, and the Munda languages of East and Central India and parts of Bangladesh. However, no evidence for this classification has ever been published.

Each of the families that is written in boldface type below is accepted as a valid clade.[clarification needed] By contrast, the relationships between these families within Austroasiatic is debated. In addition to the traditional classification, two recent proposals are given, neither of which accept traditional "Mon–Khmer" as a valid unit. However, little of the data used for competing classifications has ever been published, and therefore cannot be evaluated by peer review.

Paul Sidwell (2009a), in a lexicostatistical comparison of 36 languages which are well-known enough to exclude loan words, finds little evidence for internal branching, though he did find an area of increased contact between the Bahnaric and Katuic languages, such that languages of all branches apart from the geographically distant Munda and Nicobarese show greater similarity to Bahnaric and Katuic the closer they are to those branches, without any noticeable innovations common to Bahnaric and Katuic. He therefore takes the conservative view that the thirteen branches of Austroasiatic should be treated as equidistant on current evidence. Sidwell & Blench (2011) discuss this proposal in more detail, and note that there is good evidence for a Khasi–Palaungic node, which could also possibly be closely related to Khmuic.[6] If this would the case, Sidwell & Blench suggest that Khasic may have been an early offshoot of Palaungic that had spread westward. Sidwell & Blench (2011) suggest Shompen as an additional branch, and believe that a Vieto-Katuic connection is worth investigating. In general, however, the family is thought to have diversified too quickly for a deeply nested structure to have developed, since Proto-Austroasiatic speakers are believed by Sidwell to have radiated out from the central Mekong River valley relatively quickly.

Roger Blench (2009)[9] also proposes that there might have been other primary branches of Austroasiatic that are now extinct, based on substrate evidence in modern-day languages.

Pre-Chamic languages (the languages of coastal Vietnam prior to the Chamic migrations). Chamic has various Austroasiatic loanwords that cannot be clearly traced to existing Austroasiatic branches (Sidwell 2006).[10]

Acehnese substratum (Sidwell 2006).[10] Acehnese has many basic words that are of Austroasiatic origin, suggesting that either Austronesian speakers have absorbed earlier Austroasiatic residents in northern Sumatra, or that words might have been borrowed from Austroasiatic languages in southern Vietnam — or perhaps a combination of both.

Lepcha substratum ("Rongic").[12] Many words of Austroasiatic origin have been noticed in Lepcha, suggesting a Sino-Tibetan superstrate laid over an Austroasiatic substrate. Blench (2013) calls this branch "Rongic" based on the Lepcha autonym Róng.

Other languages with proposed Austroasiatic substrata are:

Jiamao, based on evidence from the register system of Jiamao, a Hlai language (Thurgood 1992).[13] Jiamao is known for its highly aberrant vocabulary.

Diffloth compares reconstructions of various clades, and attempts to classify them based on shared innovations, though like other classifications the evidence has not been published. As a schematic, we have:

This family tree is consistent with recent studies of migration of Y-Chromosomal haplogroup O2a1-M95. However, the dates obtained from by Zhivotovsky method DNA studies are several times older than that given by linguists.[15] The route map of the people with haplogroup O2a1-M95, speaking this language can be seen in this link.[16] Other geneticists criticise the Zhivotovsky method.

Peiros is a lexicostatistic classification, based on percentages of shared vocabulary. This means that languages can appear to be more distantly related than they actually are due to language contact. Indeed, when Sidwell (2009a) replicated Peiros's study with languages known well enough to account for loans, he did not find the internal (branching) structure below.

Other than Latin-based alphabets, many Austroasiatic languages are written with the ancient Khmer alphabet, Thai alphabet and Lao alphabet. Vietnamese divergently had an indigenous script based on Chinese logographic writing. This has since been supplanted by the Latin alphabet in the 20th century. The following are examples of past-used alphabets or current alphabets of Austroasiatic languages.

According to Chaubey et al. (2010), "AA speakers in India today are derived from dispersal from Southeast Asia, followed by extensive sex-specific admixture with local Indian populations."[22][note 1] According to Riccio et al. (2011), the Munda people are likely descended from Austroasiatic migrants from southeast Asia.[23][24] According to Zhang et al. (2015), Austroasiatic (male) migrations from southeast Asia into India took place after the last Glacial maximum, circa 10,000 years ago.[25]

^Thurgood, Graham. 1992. The aberrancy of the Jiamao dialect of Hlai: speculation on its origins and history. In Ratliff, Martha S. and Schiller, E. (eds.), Papers from the First Annual Meeting of the Southeast Asian Linguistics Society, 417-433. Arizona State University, Program for Southeast Asian Studies.

^ abSidwell (2005) casts doubt on Diffloth's Vieto-Katuic hypothesis, saying that the evidence is ambiguous, and that it is not clear where Katuic belongs in the family.

Adams, K. L. (1989). Systems of numeral classification in the Mon–Khmer, Nicobarese and Aslian subfamilies of Austroasiatic. Canberra, A.C.T., Australia: Dept. of Linguistics, Research School of Pacific Studies, Australian National University. ISBN 0-85883-373-5